PRIOR CONCURRENT THERAPY: Biologic therapy: At least 3 weeks since prior biologic therapy Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for mitomycin or nitrosoureas) Endocrine therapy: At least 2 weeks since prior endocrine therapy (except for antiandrogen therapy) Concurrent antiandrogen therapy allowed Concurrent corticosteroids allowed if stable dose for at least 2 weeks prior to study Radiotherapy: At least 3 weeks since prior radiotherapy Surgery: Not specified Other: No prior enrollment in this study At least 4 weeks since prior investigational drugs No other concurrent investigational agents